The invention relates to a novel process for the preparation of 4,4'-bis-(4-aminophenoxy)-diphenyl sulfone from 4-aminophenol and 4,4'-dihalodiphenyl sulfone in an organic solvent.
4,4'-bis-(4-aminophenoxy)-diphenyl sulfone (BAPS) is an important monomer for the preparation of high-melting polyamides, polyimides, and polyamidoimides. It is also suitable as a curing agent for epoxides.
According to DE-A-19 09 520, BAPS is prepared from p-aminophenol, sodium hydroxide solution, or potassium hydroxide solution and a 4,4'-dihalodiphenyl sulfone in an organic solvent. This is a two-stage process. First, the p-aminophenolate is prepared and the water formed is distilled off. BAPS is then obtained by the reaction of p-aminophenolate with 4,4'-dichlorodiphenyl sulfone. The product is precipitated with water, dissolved, treated with active carbon and reprecipitated. It then has a melting point of 191.degree.-192.degree. C., which can be increased to 193.degree.-194.degree. C. by recrystallization.
According to DE-A-23 15 607 (U.S. Pat. No. 3,817,921), BAPS is prepared from p-aminophenol, sodium hydroxide solution, and 4,4'-dichlorodiphenyl sulfone, stoichiometric amounts of the starting compounds being used. This is also a two-stage process. In the first stage, water is distilled off with the aid of the entraining agent chlorobenzene. After precipitation twice, a product having a melting point of 177.degree.-187.degree. C. is obtained. After recrysallization, the melting point is 188.degree.-191.degree. C.
Furthermore, according to Kawakami et al. [Journal of Polymer Science, Polymer Chemistry Edition, Vol. 12 (1974), 565-573), BApS is prepared from p-aminophenol, sodium hydroxide, and 4,4'-dichlorodiphenyl sulfone in dimethyl sulfoxide. A product having a melting point of 189.degree.-191.degree. C. is obtained. After recrystallization, the melting point is 191.degree.-192.degree. C.
For polycondensation purposes, a BAPS which is as pure as possible and has as high a melting point as possible is required. BAPS having a melting point of less than 191.degree. C. is still unsuitable, whereas a product having a melting point of 191.degree.-193.degree. C. merely leads to low-having quality polycondensates having a dark color and poor mechanical properties. Accordingly, the known processes give a BAPS which is suitable or of limited use for polycondensations only after several purification steps and after recrystallization.